1. Technical field
The present invention relates to exhaust brakes for large-size vehicles such as trucks or buses and, more particularly, to exhaust brakes for diesel powered vehicles.
2. Description of the Prior Art
Exhaust brakes for diesel powered vehicles are well known. A typical exhaust brake is additional to the regular wheel brakes allowing the driver to slow the vehicle, particularly when proceeding down steep inclines. The exhaust brake is typically mounted under the motor vehicle in the exhaust system beyond the outlet of the engine or any optional turbo-charger thereon where it is exposed to road dirt and debris. When activated, the exhaust brake restricts the escape of exhaust gases, whereby back pressure built up on the engine. The momentum of the vehicle drives the engine against the built-up back pressure causing the engine to absorb horsepower which results in reduction of vehicle's speed.
A typical exhaust brake is comprised of a housing, a "butterfly" restricter-valve and a pneumatic actuator. The restricter valve has a pivotally mounted shaft with a shield thereon. The shape of the shield is matched to a nonperpendicular inner cross-section of the housing. Due to the pivotal mounting of the shaft, the shield may rotate between closed and open positions. Typically, the angle of rotation of the shield is less than ninety degrees (90.degree.) and is limited by an adjustable abutment so that, in the closed position, a certain exhaust gas flow is guaranteed thereby limiting the back pressure on the engine.
In order to increase the braking action of the exhaust brake, users often modify the exhaust brake system by readjusting the abutment thereof and increasing the angle of rotation of the shield. However, in doing this, the permitted maximum back pressure against the engine may be exceeded creating the possibility of severe damage to the engine.
Oftentimes, the shield of the typical prior art exhaust brake may touch the housing when in its closed position. During operation, carbon build-up on the shield from the exhaust gases may cause the shield to become stuck in its closed position and thus fail to operate properly.
Another disadvantage of the typical prior art exhaust brake is that the "butterfly" restricter valve member has a symmetrical design whereby, in the event the actuator fails, the restricter valve member tends to remain in the same position as when the actuator failed.